How big might the next Grand Theft Auto be?

Take-Two Interactive Software hasn't formally announced the next installment of the massive Grand Theft Auto franchise, but it's the industry's worst kept secret.

Most industry analysts expect it to be unveiled (and released) next year – and the oddsmaking has started on exactly how big it will be. Right now, the most conservative guesses put the number just below the worldwide grosses of Titanic.

Sterne Agee analyst Arvind Bhatia says if the game does release in Take-Two's next fiscal year, it will see potential sales of up to 25 million in the first year – putting gross sales at $1.5 billion. (Titanic's worldwide gross came in at $1.84 billion, according to BoxOfficeMojo.)

The estimate is based upon sales of the last title in the series – Grand Theft Auto IV – which sold 17 million in its first year. That was April 2008. Since then, the number of PlayStation 3s and Xbox 360s has increased nearly 125 percent.

That increased installed base of players and continuing interest in the series will likely mean bigger sales. Bhatia notes that if 90 percent of GTA IV owners buy a copy of GTA V, and just 10 percent of the additional console owners buy the game, then sales would surpass 20 million units. That's a conservative outlook and could mean sales will be much higher.

Don't look for GTA or any single video game to top Avatar's numbers anytime soon, though. Worldwide grosses for that film stand at $2.8 billion.